Verification gauge for an electronic package lead inspection apparatus

ABSTRACT

A verification gauge for verifying the operation of an inspection system for inspecting the leads of an electronic package, particularly a ball grid array. The gauge has a predetermined mechanical relationship to a mechanical parameter of the leads of the electronic package so that when the inspection system is used to inspect the gauge, a reading will indicate whether the inspection system is properly set up for the mechanical parameter. The gauge may be configured to substantially emulate the structural configuration, including the particular size, shape and lead pattern, of the electronic package. The gauge may be used to verify the calibration or the predefined limit of the inspection system for the mechanical parameter, including lead coplanarity, lead pitch, missing lead and lead deformation parameters.

This application is a continuation of U.S. application Ser. No.08/995,675, filed on Dec. 22, 1997, now U.S. Pat. No. 6,084,397.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a gauge for verifying the operation ofan apparatus for inspecting leads of an electronic package, and moreparticularly to a gauge for verifying the calibration and inspectionparameters of a lead inspection apparatus for ball grid arrays.

2. Description of Related Art

The electronics industry is continually decreasing the size ofelectronic devices while increasing the pin count of the devices in aneffort to increase the density of electronic packaging. Surface mounttechnology provides the industry with the ability to continue this trendsince surface mount leads can be located relatively close to each other,as compared to through-hole technology. Common surface mount devicesinclude ball grid arrays (BGAs), quad flat packs (QFPs), flat packs,gull-wing devices and the like.

As the pin count increases and lead spacing decreases, controllingmechanical parameters of the component leads, such as lead coplanarity,lead pitch, missing leads, lead deformation and the like, is criticalfor ensuring proper electrical interconnections when the components areinstalled on a printed circuit board. Consequently, lead inspectionsystems are utilized throughout the industry, from componentmanufacturing to printed circuit board assembly, for inspecting theleads of electronic packages to ensure that they meet their dimensionalrequirements.

Conventional lead inspection systems include infrared systems, laserscanning systems, gray scale camera systems and the like. Leadinspection systems typically analyze one or more mechanical features ofan electronic package using various algorithms that compare the resultsof detector readings to predetermined parameter limits to determinewhether the component is an acceptable or an unacceptable device. Theaccuracy of inspection systems, however, may be affected by severalfactors, including system calibration and programmed inspectionparameters, that can lead to improper component acceptances and/orrejections with the potential result that a defective component isinstalled on a board or a perfectly good component is discarded asdefective.

Since system calibration may change or drift over a period of time, itis necessary that system calibration be periodically tested and adjustedto alleviate any potential problems due to an improperly calibratedsystem. Calibration methods used in the industry, which typicallyutilize optics, 3-D triangulation sensors and lasers, require aconsiderable amount of time to calibrate a system. Consequently, aninspection system may not be calibrated often enough to ensure accurateelectronic component inspections. Additionally, these calibrationmethods typically cannot be performed on-line and require a productionline shutdown.

Even when an inspection system is properly calibrated, electroniccomponents may still be improperly rejected or accepted due to aninspection process error. For example, an operator typically programs aninspection system with one or more predetermined inspection parametersto define the allowable limits against which a particular electronicpackage is compared when evaluating whether to accept or reject thecomponent. When a parameter limit is incorrectly programmed into thesystem, a component can be improperly accepted or rejected even thoughthe system calibration is accurate. Such process errors generally willnot be discovered by testing the calibration of the system.

A “golden” component, which is an actual electronic component with knowndimensions, may be used to verify the calibration and inspectionparameters of an inspection system. However, the dimensions of thegolden component leads can become altered due to handling and itsrepeated use as a verification unit. Verification units have beendeveloped that are more robust than a golden component so that the unitmay be more likely to maintain its mechanical parameters even withrepeated use and handling.

U.S. Pat. Nos. 5,489,832 and 5,477,138 to Erjavic et al. discloseverification units which resemble certain aspects of quad flat pack andplastic leaded chip carrier type packages and are used for testing thecalibration of a lead inspection system for such electronic packages.These units, however, are not suitable for verifying the calibration orprocess parameters of a lead inspection system for a ball grid array(BGA), including plastic and ceramic BGAs, micro BGAs and similar chipon board components.

In view of the foregoing, it is an object of the present invention toprovide an improved device and a method for verifying the calibrationand process parameters of a lead inspection apparatus for inspectingpredetermined mechanical parameters of a ball grid array and similarchip on board components, and a method of manufacturing the device.

SUMMARY

In one embodiment of the invention, a verification gauge is provided forverifying the operation of a lead inspection apparatus for inspectingleads of an electronic package that is comprised of a package body and aplurality of conductive leads arranged on the package body in a leadpattern. The electronic package has a predefined limit for at least onemechanical parameter of its conductive leads. The gauge has apredetermined mechanical relationship to the mechanical parameter of theconductive leads so that when the inspection system is used to inspectthe gauge, the inspection system will provide a reading that isindicative as to whether the inspection system is properly set up forthe at least one mechanical parameter.

In one illustrative embodiment of the invention, the verification gaugeincludes a gauge body having a plurality of apertures disposed on anouter surface thereof and a plurality of gauge lead members disposed inthe plurality of apertures. The apertures are arranged to correspond toat least a portion of the lead pattern of the electronic package and atleast a portion of each gauge lead member protrudes from a correspondingaperture by a predetermined amount beyond the outer surface of the gaugebody. At least one of the gauge lead members has a predeterminedmechanical relationship to at least one mechanical parameter of anelectronic package.

In another illustrative embodiment of the invention, the verificationgauge comprises a gauge body that is devoid of electronic circuitry, anda plurality of gauge balls arranged on the gauge body to correspond toat least a portion of the lead pattern, at least one of the gauge ballshaving a predetermined mechanical relationship to at least onemechanical parameter of a ball grid array.

In a further illustrative embodiment of the invention, a method ofmanufacturing the verification gauge comprises steps of providing agauge base plate having a plurality of gauge holes extendingtherethrough that are arranged to correspond to at least a portion ofthe lead pattern of a ball grid array; providing a plurality of gaugeballs; and placing the plurality of gauge balls in the plurality ofgauge holes with at least a portion of each ball protruding from anouter surface of the gauge base plate. At least one of the gauge ballshas a predetermined mechanical relationship to at least one mechanicalparameter of the ball grid array.

In another illustrative embodiment of the invention, a method forverifying the operation of an inspection system for a ball grid arraycomprises steps of providing at least one verification gauge; inspectingthe gauge with the inspection system for the at least one mechanicalparameter; and determining whether the inspection system is properly setup for detecting when the predefined limit for at least one mechanicalparameter is exceeded by a ball grid array. The verification gauge iscomprised of a gauge body that is devoid of electronic circuitry, and aplurality of gauge balls arranged on the gauge body to correspond to atleast a portion of the lead pattern, at least one of the gauge ballshaving a predetermined mechanical relationship to the at least onemechanical parameter of the ball grid array.

The gauge may be configured to substantially emulate the structuralconfiguration, including the particular size, shape and lead pattern, ofthe electronic package. The gauge may be used to verify the calibrationor the predefined limit of the inspection system for the mechanicalparameter, including lead coplanarity, lead pitch, missing lead and leaddeformation parameters. The gauge may be configured to be either“acceptable”, such that the gauge is within the predefined limit for themechanical parameter, or “nonacceptable”, such that the gauge exceedsthe predefined limit for the mechanical parameter.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and advantages of the present inventionwill become apparent with reference to the following detaileddescription when taken in conjunction with the accompanying wings inwhich:

FIG. 1 is a bottom view of an illustrative embodiment of a verificationgauge according to the present invention;

FIG. 2 cross-sectional view of the gauge taken along section line 2—2 ofFIG. 1;

FIG 3 is an enlarged view of the gauge of FIG. 2 illustrating anarrangement for controlling the amount of ball protrusion from thegauge;

FIGS. 4A-4D are schematic lead patterns for typical ball grid arrays;

FIG. 5 is a side view of an illustrative embodiment of a verificationgauge configured for assessing coplanarity parameters;

FIG. 6 is a bottom view of the gauge of FIG. 5;

FIG. 7 is a bottom view of an illustrative embodiment of a verificationgauge configured for assessing lead pitch error parameters;

FIG. 8 is an enlarged schematic view of the gauge of FIG. 7 illustratinga gauge ball that is located off grid;

FIG. 9 is a bottom view of an illustrative embodiment of a verificationgauge configured for assessing missing lead detection parameters;

FIG. 10 a cross-sectional side view of another illustrative embodimentof a verification gauge,according to the present invention;

FIG. 11 is an enlarged schematic view of the gauge of FIG. 10illustrating a gauge ball prior to being coined in a gauge base plate;and

FIG. 12 is an illustrative embodiment of a coining die set that may beused to manufacture verification gauge of FIG. 10.

DETAILED DESCRIPTION

In one illustrative embodiment of the invention shown in FIGS. 1-3, averification gauge is provided for verifying the operation of aninspection apparatus for inspecting one or more mechanical parameters ofthe leads of an electronic package. The verification gauge 20 includes agauge body 22 and a plurality gauge lead members 24 that are preciselylocated on the gauge body to establish a predetermined mechanicalrelationship with the mechanical parameters of the electronic packageleads. As discussed more fully below, the gauge 20 can be used to checkthe calibration of the inspection system or to verify the preprogrammedinspection limits for mechanical parameters that may include leadcoplanarity, lead pitch, missing leads and lead deformation. When theinspection system is used to inspect the gauge 20, the inspection systemwill provide a reading that is indicative as to whether the inspectionsystem is properly set up for one or more of the mechanical parameters.The gauge body 22 is devoid of electronic circuitry so that the gauge 20is an electronically nonfunctional device.

In one embodiment of the invention, the gauge body 22 has a plurality ofapertures 26 disposed on its outer surface 28, and the plurality ofgauge lead members 24 are disposed in the apertures 26 to protrude fromthe outer surface 28 of the body. The gauge body 22 may include a baseplate 30 with a recess 32 and a cover plate 34 that is attached to thebase plate 30 over the recess 32 to form an internal cavity 36. Theapertures 26 extend through the base plate 30 from the cavity 36 to theouter surface 28 of the body. The lead members 24 are seated in theouter end of the apertures 26 opposite the cavity 36 so that at least aportion of each lead member 24 extends beyond the outer surface 28 ofthe body.

As illustrated in FIGS. 2-3, each aperture 26 is a hole and each gaugelead member 24 is a ball that cooperates with the hole 26 in a mannerthat controls the amount of ball protrusion from the body. Each hole 26may be tapered so that its diameter decreases in a direction from thecavity 36 toward the outer surface 28 of the base plate. In particular,the diameter decreases from a first diameter at a first end 38 of thehole 26 to a second diameter at a second end 40 of the hole 26 to form alip 42 or knife edge adjacent the outer surface 28 of the plate. Thefirst diameter of the hole is greater than the ball diameter while thesecond diameter of the hole is less than the ball diameter so that theball 24 can be readily inserted into the first end 38 of the hole andretained in the base plate 30 by the lip 42 at the second end 40 of thehole.

The relative sizes between the hole 26 and the ball 24 controls theamount of ball protrusion from the gauge body 22. As the diameter of thelip 42 decreases relative to the ball diameter, the amount of ballprotrusion from the base plate 30 will also decrease. Consequently, theamount of protrusion of a ball 24 relative to the gauge body 22 and theother balls 24 may be readily established using precisely formed holesand balls of predetermined dimensions.

In one embodiment of the invention, each of the balls 24 hassubstantially the same diameter and the amount of ball protrusion iscontrolled by forming precisely dimensioned tapered holes 26. The holes26 may be formed using chemical photoetching and electropolishingprocesses. Other processes such as laser drilling may also be utilizedto form the holes. The balls 24 may be commercially available precisionground ball bearings. Preferably, the relative sizes of the holes andballs are determined so that the balls are contacted by the lip 42 ofthe hole approximately 1 to 1.5 mils below the centerline 44 of the ballto ensure that the ball is retained by the hole.

The gauge balls 24 may be fixed in the holes 26 to maintain theirpredetermined mechanical relationship to the mechanical parameters ofthe electronic package. In one embodiment, the cavity 36 is partiallyfilled with a potting compound 46 that fills each hole above the ball.The volume of potting compound 46 is preferably less than the volume ofthe cavity 36 so that, when the cover plate 34 is placed on the baseplate 30, the compound is not squeezed from the cavity and onto theinterface surfaces between the cover plate and the base plate. A vent 48may be provided through the cover plate 34 so that air may be ventedfrom the cavity when the cover plate is attached to the base plate.

As illustrated, the gauge includes twenty-five balls 24 arranged in a5×5 grid pattern of columns and rows. It is contemplated that the actualgauge ball configuration matches the particular number and pattern ofsolder balls for a BGA being inspected by a lead inspection system. Itshould be understood, however, that the gauge may be configured to matcha subset of the BGA ball pattern. Examples of various BGA ball patterns,as shown in FIGS. 4A-4D, may include an even row/column pattern (FIG.4A), an odd row/column pattern (FIG. 4B), a zone depopulation pattern(FIG. 4C), and a staggered pattern (FIG. 4D). It should be appreciatedthat a gauge can be provided to match numerous other possible leadpatterns.

In one embodiment of the invention, the base plate 30, cover plate 34and gauge balls 24 are made from a material, such as stainless steel,that ensures a structurally rugged gauge that can withstand roughhandling and repeated use without adversely affecting its accuracy. Thecover plate 34 may be precisely aligned with the base plate 30 usingtooling pins (not shown) and attached to the base plate using anadhesive (for example, a cyanoacrylate), fasteners or the like. Thepotting compound 46 for fixing the balls 24 in the gauge may be apolyurethane elastomer that can be cured at room or relatively lowtemperature. The balls 24 and the lower surface 28 of the base plate 30may be passivated or electroplated to produce a contrasting refractionindex for use with inspection systems that utilize automated visionalignment.

In one embodiment, the base plate 30 has an overall thickness ofapproximately 0.030 inches and a recess depth of approximately 0.020inches, the cover plate 34 has a thickness of approximately 0.125inches, and the vent hole 48 has a diameter of approximately 0.015-0.020inches. The upper and lower surfaces 50, 52 of the cover plate 34 may beprecision ground or lapped to be parallel to each other to within 0.0005inches, or better, so that the cover plate has minimal affect on themechanical parameters of the gauge balls, particularly when the uppersurface 50 of the gauge is used by a pick up tool of the inspectionsystem as the datum location surface. The peripheral configuration anddimensions of the gauge 20 may correspond to the particular packageconfiguration of the BGA being inspected by the inspection system.

The gauge 20 may be used as a baseline device when testing andadjusting, as necessary, the calibration of the inspection apparatus orverifying the preprogrammed inspection limits for one or more mechanicalparameters including coplanarity, lead pitch, missing lead, leaddeformation and the like. In one embodiment, the gauge 20 may beconfigured to be “acceptable” so that each mechanical parameter iswithin its allowable limit to ensure that the inspection apparatusproperly accepts a satisfactory electronic package. Conversely, thegauge 20 may be configured to be “nonacceptable” with one or moremechanical parameters outside its allowable limit to ensure that theinspection apparatus properly rejects an unacceptable electronicpackage. Additionally, a set of gauges 20 may be provided that includesa gauge that is configured as an ideal component to be used to calibratean inspection apparatus, and various “acceptable” and “nonacceptable”gauges configured to verify the calibration and inspection limits forone or more mechanical parameters of interest. Preferably, a separategauge is provided for checking each mechanical parameter. It is to beappreciated, however, that a gauge may be configured for checkingmultiple parameters of the system.

The following embodiments of the invention are presented to illustrate agauge that is suitable for verifying a particular mechanical parameterof a ball grid array (BGA), including plastic and ceramic BGAs, microBGAs and similar chip on board components. It is to be understood,however, that the embodiments are included for illustrative purposesonly and are not intended to limit the scope of the invention.

One mechanical parameter of interest for ball grid arrays is leadcoplanarity which is the distance between a seating plane and a lead ofthe device. An electronic package with leads that exceed a predeterminedamount of coplanarity can result in weak or defective solder joints.Noncoplanarity in a BGA is primarily due to nonuniformly shaped solderballs, warpage or cupping of the component package, or a combinationthese factors. When a BGA is placed ball side down on a flat surface,the tips of three balls surrounding the package center of gravity willrest on the flat surface and define the seating plane of the package.The tip of each remaining ball typically will lie above the seatingplane by an amount corresponding to its coplanarity value. As long asthe coplanarity value for each ball does not exceed a predeterminedlimit, the component is acceptable.

FIGS. 5-6 illustrate a gauge configuration that is suitable forassessing the coplanarity calibration or the programmed coplanaritylimit of an inspection apparatus. The gauge 60 includes at least threeballs 62 that protrude from their respective holes by a predeterminedamount to define a seating plane 64 for the gauge, and at least one ball66 that protrudes from its respective hole so that its tip lies abovethe seating plane 64 by a predetermined amount corresponding to adesired coplanarity value ΔZ. The balls 62 defining the seating plane 64are located on the gauge body so that they surround the center ofgravity 68 of the gauge. The ball 66 located above the seating plane 64may be located to have a coplanarity value ΔZ that either exceeds ordoes not exceed the coplanarity limit to respectively form a“nonacceptable” gauge or an “acceptable” gauge to verify the inspectionsystem on each side of the coplanarity limit. As discussed above, theamount of ball protrusion can be readily established, for example, bycontrolling the sizes of the balls and their corresponding holes. Forexample, an “acceptable” gauge and a “nonacceptable” gauge may beprovided to verify that the inspection apparatus is properly rejectingelectronic packages having a coplanarity limit of 0.008 inches, which isa typical limit allowed for a plastic BGA package. The “acceptable”gauge may be configured so that one or more balls lie approximately0.007 inches (7 mils) above the seating plane, and the “nonacceptable”gauge may be configured so that one or more balls lie approximately0.009 inches (9 mils) above the seating plane.

In one embodiment, the seating plane may be defined by at least threeballs 62 having a diameter of 30.0±0.1 mils that are disposed about thecenter of gravity 68 of the gauge in a tapered hole having a lipdiameter of 29.6±0.2 mils. The “acceptable” gauge may include one ormore balls 66 with a diameter of 30.0±0.1 mils that are disposed in atapered hole having a lip diameter of 25.4±0.2 mils to establish a gaugecoplanarity value ΔZ no greater than 7 mils. The “nonacceptable” gaugemay include one or more balls 66 with a diameter of 30.0±0.1 mils thatare disposed in a tapered hole having a lip diameter of 17.0±0.2 mils toestablish a gauge coplanarity value ΔZ of at least 9 mils. The remainingballs and holes may be configured so that the balls lie anywhere betweenthe seating plane and the established coplanarity value. The taperedholes for each of the gauge balls can have a tapered angle A (FIG. 3) ofapproximately 8° to 15° depending on the particular ball pitch of thegauge. It is to be understood that these dimensions are exemplary andthat other ball and hole sizes may be utilized to create a gauge thathas any desired coplanarity value.

Another mechanical parameter of interest for ball grid arrays is leadpitch error. Solder balls for a BGA are generally positioned relative toa two-dimensional X-Y grid to ensure that the balls will properly alignwith corresponding pads on a printed circuit board and the like toestablish a desired electrical connection between the BGA and the board.While ideally located at its basic X-Y grid coordinate, each solder ballwill generally deviate by some amount from its basic grid position dueto manufacturing process tolerances. Consequently, it is desirable tomaintain this deviation or lead pitch within a defined lead pitchtolerance to ensure proper alignment between the solder balls and theboard during the assembly process. FIGS. 7-8 illustrate a gaugeconfiguration that is suitable for assessing the lead pitch calibrationor programmed pitch value of an inspection apparatus. The gauge 70includes at least one ball 72 that is positioned relative to the X-Ygrid so that it deviates from its basic grid location 74 bypredetermined amounts ΔX, ΔY corresponding to a desired lead pitchlimit. The amount of lead pitch for each ball can be readily establishedby controlling the position of its corresponding hole since the centeraxes of the ball and hole substantially coincide due to their respectiveshapes. Each hole may be precisely located relative to the X-Y gridusing a photoetching or similar precision process.

For example, to verify that the inspection apparatus is properlyrejecting electronic packages having a lead pitch error that exceeds alimit of 4 mils, a “nonacceptable” gauge may be configured so that oneor more balls lies approximately 5 mils off the basic X-Y grid relativeto the X-axis, the Y-axis or both axes. This can be readily achieved byforming one or more holes in the base plate so that they are preciselylocated off grid 76 by desired amounts ΔX, ΔY. It is to be understoodthat these dimensions are exemplary and that other ball positions may beutilized to create a gauge that has any desired lead pitch value.

A further mechanical parameter of interest for ball grid arrays ismissing lead detection. Solder balls for a BGA are generallyindividually attached to contacts or pads on the bottom of the BGA bodyusing a solder reflow process. Due to a defective solder joint, roughhandling and the like, a solder ball may become detached from the BGApackage at some point prior to being assembled to a circuit board.

In general, a BGA missing a solder ball would be considered unacceptableand should be detected by an inspection process. However, in someinstances a BGA with one or more missing solder balls may test aselectrically functional on a circuit board. For example, a BGA that ismissing a solder ball for a signal circuit connection would likely be afatal defect detected during functional board test. Conversely, a BGAmissing a solder ball for a ground plane connection may not be detectedas the device may include a plurality of solder balls for ground planeconnections.

While one or more missing parallel ground balls may not affect theelectrical functionality of the device, the thermal conductivity throughthe missing ball is lost. Conventionally, the semiconductor die of theBGA transfers a portion of its dissipated heat through the ground ballsto the circuit planes of the board. Therefore, one or more missing ballsmay raise the operating temperature of the die and potentially affectlong-term reliability of the device. Consequently, it may be desirableto test a lead inspection system to ensure that it is properly screeningelectronic packages for missing leads prior to mounting it on a board.

FIG. 9 illustrates a gauge configuration that is suitable for assessingthe missing ball detection or the missing ball sensitivity of aninspection apparatus for a ball grid array. In one embodiment, the gauge80 includes a plurality of gauge balls 82 that, although arranged tocorrespond to the lead configuration of the electronic package, includeless than the required number of solder balls. The gauge may include oneor more missing ball regions 84, which do not contain a gauge ball 82,corresponding to a solder ball location. The missing ball regions 84 maybe located to coincide with functionally necessary solder balls (signalballs), functionally redundant solder balls (ground plane balls) or acombination of both to test the sensitivity of the inspection system.Preferably, although not necessarily, the missing ball regions 84 of thegauge also may not contain a corresponding hole. This is readilyaccomplished using a photoetching process by simply deleting the missingball region holes from the photo imaging artwork for the gauge.

Still another mechanical parameter of interest for ball grid arrays isball diameter which can be indicative of lead deformation or incorrectsolder ball size that may result in a weak or defective solder jointbetween the solder ball and its corresponding board connection.Generally, the solder balls on a BGA package should be substantiallyspherical members having substantially the same diameters. During themanufacturing process of the BGA, the size and shape of each solder ballmay inadvertently become deformed or a solder ball of incorrect size maybe inadvertently attached to the BGA package. Consequently, it may bedesirable to test a lead inspection system to ensure that it is properlyscreening BGA packages for deformed or incorrectly sized solder ballleads prior to mounting them on a board.

In one embodiment, a verification gauge suitable for assessing the balldiameter calibration or programmed diameter limit of an inspectionapparatus may be similar to the coplanarity gauge 60 described above inconnection with FIGS. 5-6. In particular, the diameter of the taperedholes 26 may be controlled to vary the effective diameter of the balls24 protruding from their corresponding holes. For example, an“nonacceptable” gauge may include one or more holes that are sized sothat the effective diameter of the portion of the balls protruding fromthe holes are undersized, oversized or a combination of both. An“acceptable” gauge may include holes that are each sized so that theeffective diameter of the portion of each ball protruding from the holesfalls within acceptable limits. It is to be understood that other gaugeconfigurations may be implemented for testing ball diameter calibrationincluding gauges using different diameter balls.

In another illustrative embodiment of the invention shown in FIGS.10-12, a verification gauge is manufactured using a coining process thatforces gauge balls a predetermined amount through a gauge base plate. Acoining process is particularly suited for making a gauge with minimalcoplanarity variations between its balls since a coining die set can bemade with highly accurate dimensions resulting in ball height variationsless than approximately 0.1 mils. Such a gauge would be useful foradjusting the coplanarity calibration since each ball essentially liesin the seating plane with zero ball coplanarity.

The verification gauge 90 includes a gauge base plate 92 having aplurality of gauge holes 94 extending therethrough, a plurality of gaugeballs 96 disposed in the holes 94 and a cover plate 98 that is attachedto the base plate 92. The gauge holes 94 and balls 96 preferably arearranged to correspond to a particular BGA solder ball pattern. Incontrast to the gauge described above, each hole 94 in this embodimentis configured as a countersunk hole (FIG. 11) that includes a taperedupper hole portion 100 and a precision lower hole portion 102. Thetapered portion 100 has a diameter and an angle B that is sufficient tocollect and locate a ball 96, and the precision hole portion 102 has adiameter that creates an interference fit sufficient to retain the ball96 in the base plate 92 when the ball is pressed through the hole.

As illustrated in FIG. 12, a coining die set 110 may include a die setbase plate 112, a ball depth plate 114, a cavity plate 116 and a topplate 118 configured to be stacked and pressed toward each other toforce the gauge balls 96 into the gauge base plate 92. The ball depthplate 114 has a plurality of guide holes 120 that are arranged tocorrespond to the gauge holes 94. Each of the guide holes 120 has adiameter that is greater than the corresponding ball diameter so thatthe depth plate 114 does not impede with coining the ball 96 in the baseplate while maintaining a precise ball pitch between adjacent gaugeballs. The thickness of the cavity plate 116 and the ball depth plate114 may be ground flat and lapped to be within millionths of a desireddimension to precisely control the amount of gauge ball protrusion fromthe gauge base plate 92 by controlling the spacing between the top plate118 and the cavity plate 116 and the spacing between the ball depthplate 114 and the die set base plate 112.

To assemble a verification gauge using the coining die set, the gaugebase plate 92 is positioned within the cavity plate 116 and on the balldepth plate 114 so that the gauge holes 94 are aligned with the guideholes 120. Precise hole alignment may be achieved using tooling holes122 on the gauge base plate 92 that mate with corresponding tooling pins(not shown) provided on the ball depth plate 114. The tooling holes 122and pins may be configured to ensure that the gauge base plate 92remains flat during the coining process. Gauge balls 96 are placed ineach of the tapered hole portions 100 and pressed through the precisionhole portions 102 using the top plate 118 until the top plate abuts thecavity plate. As the balls 96 are pressed through the gauge holes 94,the material surrounding the precision holes 102 is forced to stretchand cold form around each ball.

Once the balls 96 are coined to the gauge base plate 92, the cover plate98 is attached to the base plate 92. The balls may be secured in theirdesired position to maintain the amount of ball protrusion by partiallyfilling a cavity 124 between the cover plate 98 and base plate 92 with apotting compound 126, such as a polyurethane elastomer. The cover plate98 may be attached to the base plate 92 using an adhesive material (forexample, a cyanoacrylate), fasteners or the like. An air vent 128 may beprovided through the cover plate for venting air from the cavity 124.

In one embodiment, the gauge base plate 92 has an overall thickness ofapproximately 30 mils with the precision lower hole portion 102 having athickness of approximately 4 mils to 8 mils and the tapered upper holeportion 100 having an angle B of approximately 8° to 15°. The ball depthplate holes 120 have a diameter that is approximately 0.4 mils to 0.8mils greater than the diameter of the gauge balls 96.

Having described several embodiments of the invention in detail, variousmodifications and improvements will readily occur to those skilled inthe art. Such modifications and improvements are intended to be withinthe spirit and scope of the invention. Accordingly, the foregoingdescription is by way of example only and is not intended as limiting.The invention is limited only as defined by the following claims andtheir equivalents.

What is claimed is:
 1. A verification gauge for verifying the operationof an inspection system for inspecting leads of an electronic packagecomprised of a package body and a plurality of conductive leads arrangedon the package body in a lead pattern, the electronic package having apredefined limit for at least one mechanical parameter of the conductiveleads, the verification gauge comprising: a gauge body having aplurality of gauge holes disposed on an outer surface thereof, the gaugeholes extending through a portion of the gauge body and being arrangedto correspond to at least a portion of the lead pattern of theelectronic package; and a plurality of gauge lead members disposed inthe plurality of gauge holes, the plurality of gauge holes cooperatingwith the plurality of gauge lead members to maintain at least a portionof each gauge lead member protruding from a corresponding gauge hole bya predetermined amount beyond the outer surface of the gauge body, atleast one of the gauge lead members having a predetermined mechanicalrelationship to the at least one mechanical parameter so that when theinspection system is used to inspect the verification gauge, theinspection system will provide a reading that is indicative as towhether the inspection system is properly set up for the at least onemechanical parameter.
 2. The verification gauge recited in claim 1,wherein the gauge body is constructed and arranged to substantiallyconform to the shape of the package body.
 3. The verification gaugerecited in claim 2, wherein the gauge lead members are constructed andarranged to substantially conform to the shapes of the conductive leads.4. The verification gauge recited in claim 3, wherein the electronicpackage is a ball grid array and the portion of each gauge lead memberextending from the outer surface is spherically shaped.
 5. Theverification gauge recited in claim 1, wherein the plurality of gaugelead members is less than the plurality of conductive leads.
 6. Theverification gauge recited in claim 5, wherein the plurality of gaugeholes is equal to the plurality of gauge lead members.
 7. Theverification gauge recited in claim 1, wherein the gauge body and theplurality of gauge lead members are constructed and arranged to maintainthe predetermined mechanical relationship of the at least one gauge leadmember to the at least one of the mechanical parameters when the gaugeis subjected to repeated use and rough handling.
 8. The verificationgauge recited in claim 1, wherein the at least one mechanical parameterincludes ball coplanarity, ball pitch, missing ball and balldeformation.
 9. The verification gauge recited in claim 1, wherein theouter surface of the gauge body and the plurality of gauge lead membershave a contrasting refraction index.
 10. A method of manufacturing averification gauge for verifying the operation of an inspection systemfor inspecting leads of a ball grid array comprised of a package bodyand a plurality of conductive balls arranged on the package body in alead pattern, the ball grid array having a predefined limit for at leastone mechanical parameter of the conductive balls, the method comprisingsteps of: (a) providing a gauge base plate having a plurality of gaugeholes extending therethrough that are arranged to correspond to at leasta portion of the lead pattern of the ball grid array; (b) providing aplurality of gauge balls; and (c) placing the plurality of gauge ballsin the plurality of gauge holes with at least a portion of each gaugeball protruding from an outer surface of the gauge base plate, at leastone of the gauge balls having a predetermined mechanical relationship tothe at least one mechanical parameter so that when the inspection systemis used to inspect the verification gauge, the inspection system willprovide a reading that is indicative as to whether the inspection systemis properly set up for the at least one mechanical parameter of the ballgrid array.
 11. A method for verifying the operation of an inspectionsystem for inspecting leads of a ball grid array comprised of a packagebody and a plurality of conductive balls arranged in a lead pattern, theball grid array having a predefined limit for a plurality of mechanicalparameters of the conductive balls, the method comprising steps of: (a)providing a plurality of verification gauges, each verification gaugecomprised of a gauge body that is devoid of electronic circuitry, and aplurality of gauge balls arranged on the gauge body to correspond to atleast a portion of the lead pattern, at least one of the gauge ballshaving a predetermined mechanical relationship to at least one of theplurality of mechanical parameters so that when the inspection system isused to inspect the verification gauge, the inspection system willprovide a reading that is indicative as to whether the inspection systemis properly set up for the at least one of the plurality of mechanicalparameters of the ball grid array, wherein at least one of thepredetermined mechanical relationship and the mechanical parameter isdifferent for each of the verification gauges; (b) inspecting at leastone of the gauges with the inspection system for the at least one of theplurality of mechanical parameters; and (c) determining whether theinspection system is properly set up for detecting when the predefinedlimit for the at least one of the plurality of mechanical parameters isexceeded by the ball grid array.
 12. The method recited in claim 11,wherein step (c) includes determining whether the inspection system isproperly set up for inspecting at least one of ball coplanarity, ballpitch, missing ball and ball deformation.
 13. The method recited inclaim 12, wherein step (c) includes determining whether the inspectionsystem is properly calibrated for the at least one mechanical parameter.14. The method recited in claim 12, wherein step (c) includesdetermining whether the inspection system is properly programmed withthe predefined limit for the at least one mechanical parameter.
 15. Themethod recited in claim 12, wherein step (c) includes adjusting at leastone of the calibration and the predefined limit of the inspection systemfor the at least one mechanical parameter based on the predeterminedmechanical relationship.
 16. The verification gauge recited in claim 1,wherein the plurality of gauge lead members includes a plurality ofgauge balls disposed in the plurality of gauge holes.
 17. Theverification gauge recited in claim 16, wherein each of the plurality ofgauge holes has a diameter, the diameter of at least one gauge holebeing different than the diameter of the other gauge holes so that thegauge ball disposed in the at least one gauge hole protrudes from thegauge body by an amount that is different than the other gauge balls.